This way we can be fairly certain we run tests of lower-level
parts of the library before we run tests of higher-level more
complex parts.  If there is any problem in a lower-level part
of the library, the earlier test will identify it and stop,
making it easire to troubleshoot the failure.

A rough naming guide has been added for the test suite to
explain the current category structure.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>